15 June 2014

Charting the rise and fall of Antarctica's prehistoric penguin populations

Adelie penguins.
Photo credit: Dr Tom Hart.
ANTARCTICA - A study of how penguin populations have changed over the last 30,000 years has shown that between the last ice age and up to around 1,000 years ago penguin populations benefitted from climate warming and retreating ice. This suggests that recent declines in penguins may be because ice is now retreating too far or too fast.

An international team, led by scientists from the University of Southampton and the University of Oxford in the UK and the Woods Hole Oceanographic Institution (WHOI) in the USA, has used a genetic technique to estimate when current genetic diversity arose in penguins and to recreate past population sizes.

Looking at the 30,000 years before human activity impacted the climate, as Antarctica gradually warmed, they found that three species of penguin - chinstrap, Adélie and southern populations of gentoo - increased in numbers. In contrast, gentoo penguins on the Falkland Islands were relatively stable, as they were not affected by large changes in ice extent.

A report of the research is published in Scientific Reports.

Chinstrap penguin.
Photo credit: Dr Tom Hart.

Lead author of the paper, Gemma Clucas from Ocean and Earth Sciences at the University of Southampton, said, "Whereas we typically think of penguins as relying on ice, this research shows that during the last ice age there was probably too much ice around Antarctica to support the large populations we see today.

“The penguins we studied need ice-free ground to breed on and they need to be able to access the ocean to feed. The extensive ice-sheets and sea ice around Antarctica would have made it inhospitable for them.

"What is particularly interesting is that after the ice age, all of these penguin populations were climate change 'winners', that is to say the warming climate allowed them to expand and increase in number.

“However, this is not the pattern we're seeing today. Adélie and chinstrap penguins appear to be declining due to climate change around the Antarctic Peninsula, so they've become 'losers'. Only the gentoo penguin has continued to be a 'winner' and is expanding its range southward."
               
To estimate changes in penguin genetic diversity, the researchers collected feathers and blood samples from 537 penguins in colonies around the Antarctic Peninsula. The scientists then sequenced a region of mitochondrial DNA that evolves relatively quickly. Using the rate of mutation of this region of DNA as a calibration point, the researchers were able to chart how the size of these populations has varied over time.

Dr Tom Hart of the University of Oxford's Department of Zoology, an author of the paper, said, "We are not saying that today's warming climate is good for penguins, in fact the current decline of some penguin species suggests that the warming climate has gone too far for most penguins.

"What we have found is that over the last 30,000 years different penguin species have responded very differently to a gradually warming world, not something we might expect given the damage current rapid warming seems to be doing to penguins' prospects.

"During the last ice age Antarctica was encircled by 100 per cent more winter sea ice than today.
As ice retreated, these penguins had access to more breeding sites and more open ocean to feed."

Gentoo penguins.
Photo credit: Gemma Clucus
Clucas said, "Despite historic warming clearly opening up new opportunities for penguins, we should not assume that current rapid warming caused by human activity is good for penguins as a whole.

“Evidence from other studies shows that climate change today is creating lots of losers and few winners – with chinstrap and Adélie populations around the Antarctic Peninsula declining fast.

“This is probably as a result of reductions in sea ice causing stocks of the krill they feed on to shrink, whilst populations of Gentoo penguins, which don't rely on krill as much, grow and expand," she said.

The underside of sea ice serves as a nursery for young krill, shrimp-like crustaceans that feed on algae growing beneath the ice. Decreased sea ice in the Antarctic Peninsula over the past 50 years has brought a reduction in krill.

"There may be more breeding habitat available now, but there may not be enough food available to sustain those penguin populations which are declining, especially in the Antarctic Peninsula where the warming is the most severe," said co-author Michael Polito, a WHOI post-doctoral investigator.

In contrast, gentoo penguin populations continue to grow. Gentoo penguins forage on a variety of prey. Scientists believe this species may be able to better adapt to shortages in krill, because of their flexible diet.

"What we are seeing is a 'reversal of fortunes' where increased warming is no longer good for two out of the three species of Antarctic Peninsula penguins. This research shows quite clearly how a single environmental change, in this case warming, can have different consequences over time," said Polito.

Within the genetic study of the gentoo species, the scientists saw a variation in population growth between those living north and south of the Antarctic Polar Front, the oceanic dividing line where the cold southern Antarctic waters meet the warmer Atlantic, Pacific, and Indian oceans.

Following the last Ice Age, the southern gentoo penguin populations grew at a faster rate than the northern populations. This is most likely because the climate and conditions in the warmer, northern nesting sites did not change as dramatically as the colder, southern sites.

"Without a good understanding of how things were in the past, it's hard to put what we see now into context. This study gives us a historic perspective on a current phenomenon," said Polito.

Sources
Rise and fall of prehistoric penguin populations charted [press release], 12 June 2014, University of Southhampton
Climate change winners and losers [press release], 12 June 2014, Woods Hole Oceanographic Institution




Scientific Journal citation Clucas GV, Dunn MJ, Dyke G, Emslie SD, Levy H, Naveen R, Polito MJ, Pybus OG, Rogers AD, Hart T (2014). A reversal of fortunes: climate change ‘winners’ and ‘losers’ in Antarctic Peninsula penguins. Scientific Journals 4, Article number: 5024. doi:10.1038/srep05024

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